EP0063213B1

EP0063213B1 - Ph electrode

Info

Publication number: EP0063213B1
Application number: EP82101033A
Authority: EP
Inventors: Junichi C/O Osaka Works Of Sumitomo Hiramoto; Shinichi C/O Osaka Works Of Sumitomo Ohkawa
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1981-02-17
Filing date: 1982-02-11
Publication date: 1987-06-03
Also published as: AU553920B2; CA1187138A; JPS57136158A; US4444644A; DE3276497D1; EP0063213A2; EP0063213A3; AU8051482A

Description

The invention relates to a PH detecting apparatus according to the prior art portion of the claim.
Figure 1 shows one embodiment of a conventional PH measuring circuit using a glass electrode. In Figure 1, reference numeral 1 designates a PH meter (or a potentiometer); 2, electrolyte; 3, a reference electrode; and 4, a glass electrode. In order to electrically measure the PH value of the electrolyte, the PH meter using the glass electrode 4 has been extensively employed because its PH measurement range is wide and its measurement accuracy is high. The glass electrode 4 is in the form of a ball or a tube (whose diameter is 5 to 10 mm) made of a glass film in which a buffer solution whose PH value is known, and an electrode, are sealed. The potential difference between the glass electrode 4 and the reference electrode 3, which are inserted into the electrolyte 2, is a certain relation to the PH value of the electrolyte 2. Therefore, the PH value of the electrolyte 2 can be determined by measuring the potential difference with the PH meter.
In Figure 2 another conventional PH measuring circuit is shown using an ISFET, as for example disclosed in the GB-A-2077439. In Figure 2, reference numeral 5 designates the ISFET; and 6, a constant current source. Only recently have ISFETS been developed, and it has been known that the PH value of an electrolyte can be measured with an ISFET. When, under the condition that the ISFET is inserted into the electrolyte 2, a predetermined voltage +V is applied to the source S of the ISFET and current is allowed to flow between the source S and the drain D thereof from the constant current source 6, the value of the voltage will depend on the PH value of the electrolyte 2. Therefore, the PH value of the electrolyte 2 can be measured by providing a voltage between the drain D and the reference electrode 3 as an output Vo_ut. However, in order to measure the PH value with an ISFET, it has been necessary to provide the constant current source (6). ' Therefore, measurement could not be achieved using the PH measuring circuit with the conventional glass electrode.
From the IEEE transactions of electrolyte devices Volume ED-26, Nr. 12, December 1979, pages 1939 to 1944, a PH measuring apparatus having the features of the generic clause of the claim 1 is known. In this document the ISFET is located at one end of a glass tube. The circuits comprising an operational amplifier and an operating DC source are located outside of the glass tube and the electrode and are not adapted to be used with a conventional PH meter.
It is an object of the present invention to provide a PH electrode using an ISFET, which can be used in a PH meter in place of a conventional glass electrode.
These objects are achieved by a PH detecting apparatus, with the features of the claim.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

Brief Description of the Drawings

In the accompanying drawings:

Fig. 1 is an explanatory diagram showing a conventional PH measuring circuit using a glass electrode;
Fig. 2 is also an explanatory diagram showing another conventional PH measuring circuit using an ISFET;
Fig. 3 is an explanatory diagram showing a PH measuring circuit which uses a PH electrode with an ISFET according to the invention;
Fig. 4 is a circuit diagram of the PH electrode with the ISFET according to the invention; and
Fig. 5 is a front view, partly in section, showing the arrangement of one example of the PH electrode according to the invention.

Detailed Description of the Preferred Embodiments

Fig. 3 illustrates a PH measuring circuit with a PH electrode using an ISFET according to this invention. In Fig. 3, reference numeral 7 designates the PH electrode using the ISFET, which incorporates a DC-source. As is apparent from a comparison of Figs. 1 and 3, the PH measuring circuit in Fig. 3 can be obtained by replacing the glass electrode 4 by the PH electrode 7. That is, the PH electrode 7 can be used in the conventional PH measuring circuit to replace the extensively used glass electrode 4.
Fig. 4 is a circuit diagram showing the PH electrode including the ISFET according to the invention. In Fig. 4, reference numeral 5 designates the ISFET; 8, a hybrid IC; and 12, the DC-source. The hybrid IC 8 includes a transistor 9, an operational amplifier 10 and a resistor 11. The voltage developed according to the PH value of the electrolyte to be measured is provided at the collector of the transistor 9, and is detected through a connector.
Fig. 5 shows one example of the PH electrode using the ISFET according to the invention. In Fig. 5, reference numeral 5 designates the ISFET; 8, the hybrid IC; 12, the DC-source; 13, a housing; 14, a cover which is threadedly engaged with the housing 13; 15, a retaining lever; 17, lead wires; 18, a glass tube; and 19, a cord. The hybrid IC 8 is built into the housing. The ISFET 5 is set at the end of the glass tube 18 which extends from the bottom of the housing 13. A part of the glass tube 18 is inserted into the electrolyte to be measured. The cord 19 is a single wire, and the connector may be the same as that connected to a commercially available PH electrode.
As may be seen from the foregoing, the aforementioned objects have been simply and efficiently attained. The ISFET PH detection of the invention incorporates the familiar cell containing tube structure including a glass tube, and is fully interchangeable with existing PH detection equipment.

Claims

A PH detecting apparatus comprising:
an electrode (7) including an ion-sensitive field- effect transistor (ISFET 5), located at one end of a tube made of insulated material (18), and

a circuit (8) with an operational amplifier (10) and an operating DC source (12) connected with the ISFET for developing a voltage according to a PH value of an electrolyte (2) to be measured,

characterized in that said tube (18), comprising said ISFET (5) at the one end, is connected at the other end thereof with a housing (13) in which said DC source (12) and said circuit (8) are mounted, and that said ISFET (5) is connected through lead wires (17) to the DC source (12) and that said circuit (8) further comprises a resistor (11), connected to one side of said DC source (12), the other side of DC source (12) being connected with the ISFET (5) and that a transistor (9) is connected between said resistor (11), said operational amplifier (10) and said ISFET (5), an output being taken from the junction of the collector of said transistor (9) and the drain of said ISFET (5) and being supplied to a conventional potential difference type PH meter (7) by means of a single wire cord (19).